(1) Field of the Invention
The present invention is directed to sensors, and more specifically to an electronic sensor which detects and measures external magnetic fields.
(2) Description of the Prior Art
The emergence of practical sensors using the giant magneto-impedance (GMI) effect has become well known. Tiny fibers smaller than a human hair that are made from a chemical composite such as cobalt, iron, silicon and boron exhibit the GMI property of a changing impedance under the influence of an external magnetic field when the fiber is excited by a radio-frequency signal. Amorphous cobalt-rich ribbons, wires, and glass covered micro-wires are good candidates for GMI applications.
Sensors that detect magnetic fields using GMI fibers can detect and record the magnetic characteristics of a small marine craft using a GMI fiber as small as a few millimeters. Current designs for such sensors typically utilize the reactance or even the resistive portion of the dynamic impedance of such fibers as the frequency-determining elements of an oscillator. One difficulty arises when, at very high resonant frequencies, the oscillator drift assumes a magnitude that is significant with respect to the frequency change that is being measured to detect the magnetic field. What is needed is a sensor that detects magnetic fields using GMI fibers that is not affected by oscillator drifts.